The objectives of the proposed work are to gather information on the structure, chemical composition, and functional significance of normal and abnormal Z-lines of muscle tissue. A further objective, related to the above, is to explore the nature of communication which exists between muscles and other systems of the body. In keeping with these objectives, then, we propose to: (1) determine if tenotomy of rat soleus muscle induces changes in older animals, as it does in younger, rapidly growing animals; (2) determine if there are any differences in the protein composition of the Z-lines of normal and tenotomized muscle; (3) determine if the various morphologically anomaaous Z-lines in tenotomized muscle have a basic, recognizable structural pattern; and (4) determine if different information from the muscle itself is an important factor for the genesis of anomalous Z-lines in tenotomized muscle.